Portable back massager



FIG. 1 is a front, top and side perspective view of a portable back massager showing my new design;

FIG. 2 is a top plan view thereof, the bottom view being a mirror image of the top view shown in FIG. 2;

FIG. 3 is a front elevation view thereof, the rear view being a mirror image of the front view shown in FIG. 3; and,

FIG. 4 is a side elevation view thereof, the side opposite being a mirror image of the side view shown in FIG. 4. 

The ornamental design for a portable back massager, as shown and described. 